Hitherto, as a device that notifies the driver of congestion information, an “onboard traffic warning device” is known (Japanese Unexamined Patent Application Publication No. 2009-87249) that receives information from outside regarding areas on a road where accidents due to traffic congestion frequently occur (frequent congestion accident areas), and when the current position of the vehicle itself is within a frequent congestion accident area, determines whether or not the vehicle itself is a congestion tail from the vehicle speed of the vehicle itself and the distance from a following vehicle, and if the vehicle itself is a congestion tail, the position of the vehicle itself is broadcast to other surrounding vehicles as the congestion tail position.
However, devices hitherto will not function without a map database indicating the frequent congestion accident areas and cannot notify other surrounding vehicles of the congestion tail information in cases in which congestion has occurred in an area lacking information stating that the area is a frequent congestion accident area.